Existing highway signs, fences, lights, and guardrails frequently utilize a two-part support post. For instance, in the installation of road signs, a stub post is first placed in the ground with one end projecting four to eight inches above the ground. A flange is formed on or slipped over and attached to the projecting end of the stub post. The signpost has a corresponding flange that is then bolted to the stub post flange. If it becomes necessary to change the signpost, a new signpost can be quickly bolted to the stub post. When a signpost is subjected to a strong lateral load, e.g., the impact of a motor vehicle, the shear force will cause the bolts to fail, allowing the signpost to break from the stub post. One drawback of this type of installation is that the stub post and flange are frequently damaged or destroyed if the bolts are over-torqued when they are installed. This necessitates digging out and replacement of the stub post.
One proposed method for overcoming this drawback utilizes a concrete anchor placed into the ground and having bolt inserts cemented in place. Bolts that are designed to break when subjected to a predetermined amount of torque are placed through the signpost flange and threaded into the insert. This method has several disadvantages. First, because overtightening of the bolts will cause them to fail, installation must be accomplished by crews trained on proper torquing procedures. In addition, special torquing tools must be used to properly install the bolts. Furthermore, the bolt inserts tend to fill with water, dirt, adn other foreign matter, complicating the reinstallation of a damaged signpost. Finally, existing slip-based stub posts cannot be easily converted to this method because of the requirement that a concrete anchor be used.